In the prior art to which this invention relates, there have been provided ultrasonic devices attached to the rear of vehicles, such as trucks to measure the distance between the rear end, tail-gate or other portions of the vehicle and a loading platform as an example. Other vehicles have been provided with ultra-sonic listening devices for warning when the noise level of an exterior object reaches a level indicative of collision possibilities. Some of the prior art systems use a plurality of transducers located around the sides of the vehicle and are connected to transmitters for sending sonic or electromagnetic pulses to distant objects. Each transmitter is correlated with a receiver for detecting sonic or electromagnetic reflected echoes from objects close by. The output of each receiver may be connected to individual indicator lamps and/or a warning device such that if any of the lamps is energized, the driver is warned that one or the other side of the vehicle is in danger of a possible collision. Other prior art devices in this art utilize mechanical means for switching the transmitter and receiver on and off, during the transmit or receive cycles, while yet other devices utilize radar systems or use a signal beacon type system for detection of objects. However, none of the prior art systems known to applicant utilize microelectronic digital logic circuitry and techniques to transmit and acquire returned echo signals converted to voltage signals to effectuate the measurement of time-to-distances of objects at discrete distances or within discrete distance ranges for display by processing such voltage signals with digital logic circuits and techniques to provide three forms of warning aids simultanously from the same echoed signals with a high degree of accuracy.
Reference to the following prior art patents will indicate the general state of the art as they may relate to the present invention as examples:
U.S. Pat. No. 3,842,397, to Thomas Sindle, issued Oct. 15, 1974; U.S. Pat. No. 3,975,708, to Joe F. Lusk, issued Aug. 17, 1976; U.S. Pat. No. 3,944,981, to Shigeyuki Akita, issued Mar. 16, 1976; U.S. Pat. No. 4,015,232, to Thomas Sindle, issued Mar. 29, 1977; U.S. Pat. No. 4,278,962, to Pin-Houn Lin, issued Jul. 14, 1981; U.S. Pat. No. 4,349,823, to Katsutoshi Tagami, issued Sep. 14, 1982; and U.S. Pat. No. 4,626,849, to John C. Sims, issued Dec. 2, 1986.